1. Technical Field
The present invention relates to a sliding material for sliding elements, wherein the sliding material comprises a thermoplastic matrix material and a PTFE (polytetrafluorcethylene) additive. In addition, the invention relates to a sliding element and a plain bearing.
2. Related Art
Maintenance-free sliding elements, such as plain bearings, are often made of multilayer materials. A porous sintered layer is applied to a support medium, which is usually realized as a steel backing. This porous and mostly metallic component is in turn impregnated with a lubricating material, and also covered by the same. Two different types are recognized, depending on the nature of the matrix polymer of the sliding material: sliding materials based on PTFE, and sliding materials based on plastics which can be treated thermoplastically (abbreviated thermoplastics), wherein the latter are of relevance here.
The sliding layers, consisting of thermoplastic sliding materials, are either provided with recesses to hold an amount of lubricant with long-term efficacy, or they are used in the form of a compound which is modified with lubricants.
It has been found that some of these types of material, with theft plastic sliding surfaces, are advantageous over purely metallic bearing materials in media-lubricated applications, such as pumps or hydraulic shock absorbers, because of their good shape matching and dirt holding capacity, as well as theft high wear resistance. In this case, the PTFE-based materials are characterized by a particularly low friction coefficient when lubricated by the media, whereas thermoplastic materials can be very resistant to wear. Suitable modified thermoplastic layers can significantly exceed the wear and load resistance of PTFE based coatings, but have a significantly higher coefficient of friction with lubrication media despite their modification.
As such, thermoplastic bearing materials have been used for many years in highly wear-intensive media-lubricated applications. DE 102 26 264 B4 describes, for example, a modified PEEK material specially developed for high temperatures, having high wear resistance. However, it is not possible when this material is used to reach the low coefficient of friction of PTFE-based materials with media lubrication.
From DE 198 08 540 B4, materials based on thermoplastics are known which have more favorable friction values than conventional thermoplastic bearing materials, because of a relatively high PTFE content and due to the avoidance of hard additives, but which are still significantly higher than those of the materials based on PTFE.
However, there is a limit to how much PTFE can be incorporated, because too high a proportion weakens the thermoplastic matrix, which in turn has a negative effect on the wear resistance of the material.
To solve this problem, DE 10 2008 055 195 B4 suggests producing a PTFE gradient by impregnating the material with a PTFE dispersion, such that it is possible to significantly reduce the coefficient of friction, especially in the outer region of the sliding layer. However, this reduces the wear resistance. A further disadvantage of this approach is the combined method in which first powder, then a liquid must be applied to a strip material, which requires increased outlay for machinery.